1. Field of the Invention
The present invention relates to a thin film transistor (TFT) array substrate for an X-ray detector and a method of fabricating the same, and more particularly, to an X-ray detector having improved sensitivity.
2. Description of the Related Art
In the X-ray diagnostic detection technique, widely used in the medical field, X-ray film is used as a medium for detecting X-rays to produce photographic images, and time consuming film-processing procedures are required to obtain the results. However, recently developed semiconductor techniques have increasingly advanced digital X-ray imaging devices. Digital X-ray detectors employing thin film transistors as switching elements have the significant advantage of providing real time imaging that speeds diagnosis.
An X-ray detector is provided with a TFT array on a TFT array substrate. Unlike a liquid crystal display (LCD), however, the X-ray detector is provided with a positive-intrinsic-negative (“PIN”) photodiode array having pixels, each pixel including a silicon layer doped with p-type impurities, an undoped silicon layer, a silicon layer doped with n-type impurities, and two electrodes for applying voltages to opposite ends of the silicon layers. The X-ray detector is different from the LCD where images are displayed by image signals externally applied and transmitted to a pixel electrode. In the X-ray detector, electrons generated from the PIN photodiode using externally induced X-rays are transmitted outside by applying a bias voltage to convert light into electric signals.
An ideal X-ray detector must have maximum sensitivity for recognizing light. Increasing the fill factor, the ratio of the area of the pixel sensitive to light, is limited by conventional design rules of the X-ray detector. Therefore, in order to increase the light sensitivity by increasing the fill factor of the X-ray detector, new design rules are desired. Further, the fill factor may be defined as the ratio of the area of the PIN diode to the area of the pixel area.